U.S. patent application number 16/659329 was filed with the patent office on 2020-02-13 for operating a fingerprint sensor comprised of ultrasonic transducers.
This patent application is currently assigned to InvenSense, Inc.. The applicant listed for this patent is InvenSense, Inc.. Invention is credited to Etienne DE FORAS, Bruno W. GARLEPP, Michael H. PERROTT, James Christian SALVIA, Hao-Yen TANG.
Application Number | 20200050817 16/659329 |
Document ID | / |
Family ID | 58765915 |
Filed Date | 2020-02-13 |
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United States Patent
Application |
20200050817 |
Kind Code |
A1 |
SALVIA; James Christian ; et
al. |
February 13, 2020 |
OPERATING A FINGERPRINT SENSOR COMPRISED OF ULTRASONIC
TRANSDUCERS
Abstract
In a method for operating a fingerprint sensor comprising a
plurality of ultrasonic transducers, a first subset of ultrasonic
transducers of the fingerprint sensor are activated, the first
subset of ultrasonic transducers for detecting interaction between
an object and the fingerprint sensor. Subsequent to detecting
interaction between an object and the fingerprint sensor, a second
subset of ultrasonic transducers of the fingerprint sensor are
activated, the second subset of ultrasonic transducers for
determining whether the object is a human finger, wherein the
second subset of ultrasonic transducers comprises a greater number
of ultrasonic transducers than the first subset of ultrasonic
transducers.
Inventors: |
SALVIA; James Christian;
(Belmont, CA) ; TANG; Hao-Yen; (San Jose, CA)
; PERROTT; Michael H.; (Nashua, NH) ; GARLEPP;
Bruno W.; (Sunnyvale, CA) ; DE FORAS; Etienne;
(Saint Nazaire les Eymes, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
InvenSense, Inc. |
San Jose |
CA |
US |
|
|
Assignee: |
InvenSense, Inc.
San Jose
CA
|
Family ID: |
58765915 |
Appl. No.: |
16/659329 |
Filed: |
October 21, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15354876 |
Nov 17, 2016 |
10452887 |
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16659329 |
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62334392 |
May 10, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06K 9/00067 20130101;
G06K 9/0002 20130101; G06F 3/0436 20130101; G06F 1/3231 20130101;
G06F 1/3287 20130101 |
International
Class: |
G06K 9/00 20060101
G06K009/00; G06F 1/3287 20060101 G06F001/3287; G06F 1/3231 20060101
G06F001/3231; G06F 3/043 20060101 G06F003/043 |
Claims
1. A method for operating a fingerprint sensor comprising a
plurality of ultrasonic transducers, the method comprising:
activating a first subset of ultrasonic transducers of the
fingerprint sensor, the first subset of ultrasonic transducers for
detecting interaction between an object and the fingerprint sensor;
and subsequent to detecting interaction between an object and the
fingerprint sensor, activating a second subset of ultrasonic
transducers of the fingerprint sensor, the second subset of
ultrasonic transducers for determining whether the object is a
human finger.
2. The method of claim 1, further comprising: responsive to
determining that the object is a human finger, capturing an image
of a fingerprint of the finger.
3. The method of claim 2, wherein the image of the fingerprint is
captured using at least the second subset of ultrasonic
transducers.
4. The method of claim 2 further comprising: responsive to
capturing the image of a fingerprint of the finger, entering a
sleep mode for a predetermined period; and after the predetermined
period, performing the activating the first subset of ultrasonic
transducers of the fingerprint sensor.
5. The method of claim 1, wherein the ultrasonic transducers are
Piezoelectric Micromachined Ultrasonic Transducer (PMUT)
devices.
6. The method of claim 1, further comprising: responsive to not
detecting interaction between an object and the fingerprint sensor,
entering a sleep mode for a predetermined period; and after the
predetermined period, performing the activating the first subset of
ultrasonic transducers of the fingerprint sensor.
7. The method of claim 6, wherein the activating a first subset of
ultrasonic transducers of the fingerprint sensor is performed
periodically until interaction between an object and the
fingerprint sensor is detected.
8. The method of claim 1, wherein the activating the first subset
of ultrasonic transducers of the fingerprint sensor comprises:
capturing at least one pixel using the first subset of ultrasonic
transducers; comparing a signal of the at least one pixel to a
threshold; and provided the signal is outside the threshold,
determining that interaction between an object and the fingerprint
sensor is detected.
9. The method of claim 1, wherein the activating the second subset
of ultrasonic transducers of the fingerprint sensor comprises:
capturing a plurality of pixels arranged to detect characteristics
of a fingerprint on the object; determining whether the plurality
of pixels comprises characteristics of a fingerprint; and provided
the plurality of pixels comprises characteristics of a fingerprint,
determining that the object is a human finger.
10. A method for operating an ultrasonic sensor comprising a
plurality of ultrasonic transducers, the method comprising:
capturing at least one pixel using a subset of ultrasonic
transducers of the plurality of ultrasonic transducers of the
ultrasonic sensor; comparing a signal of the at least one pixel to
a threshold; and provided the signal is outside the threshold,
determining that interaction between an object and the ultrasonic
sensor is detected.
11. The method of claim 10, wherein the plurality of ultrasonic
transducers is arranged into a plurality of blocks, and wherein the
capturing the at least one pixel using the subset of ultrasonic
transducers comprises: capturing at least one pixel for at least
two blocks of the plurality of blocks.
12. The method of claim 11, wherein the comparing a signal of the
at least one pixel to a threshold and the determining that
interaction between an object and the ultrasonic sensor is detected
are performed for at least two blocks of the plurality of
blocks.
13. The method of claim 12, wherein a determination that
interaction between an object and the ultrasonic sensor is detected
is made provided the signal is outside the threshold for at least
two blocks of the plurality of blocks.
14. The method of claim 10, wherein the threshold comprises an
offset and a range.
15. The method of claim 14, further comprising: responsive to
determining that the object is not a human finger, updating the
offset of the threshold with the signal.
16. The method of claim 10, wherein the threshold comprises a range
from a low threshold to a high threshold.
17. A method for operating an ultrasonic sensor comprising a
plurality of ultrasonic transducers, the method comprising:
determining whether an object is interacting with the ultrasonic
sensor; responsive to determining that an object is interacting
with the ultrasonic sensor, determining whether the object is a
human finger, wherein the determining whether the object is a human
finger comprises: capturing a plurality of pixels of the object
interacting with the ultrasonic sensor using a subset of ultrasonic
transducers of the plurality of ultrasonic transducers of the
ultrasonic sensor, the plurality of pixels arranged to detect
characteristics of a fingerprint on the object; determining whether
the plurality of pixels comprises characteristics of a fingerprint;
and provided the plurality of pixels comprises characteristics of a
fingerprint, determining that the object is a human finger.
18. The method of claim 17, wherein the plurality of pixels are
arranged in orthogonal vectors.
19. The method of claim 17, wherein the plurality of ultrasonic
transducers is arranged into a plurality of blocks, and wherein the
capturing the plurality of pixels arranged to detect
characteristics of a fingerprint on the object comprises: capturing
orthogonal vectors of pixels for at least one block of the
plurality of blocks.
20. The method of claim 17, wherein the determining whether the
plurality of pixels comprises characteristics of a fingerprint
comprises: determining whether the plurality of pixels is
indicative of ridge/valley pattern.
Description
RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of
co-pending U.S. patent application Ser. No. 15/354,876, filed on
Nov. 17, 2016, entitled "OPERATING A FINGERPRINT SENSOR COMPRISED
OF ULTRASONIC TRANSDUCERS," by Salvia, et al., having Attorney
Docket No. IVS-684, and assigned to the assignee of the present
application, which is incorporated herein by reference in its
entirety.
[0002] U.S. patent application Ser. No. 15/354,876 claims priority
to and the benefit of then co-pending U.S. Provisional Patent
Application No. 62/334,392, filed on May 10, 2016, entitled
"ALWAYS-ON SENSOR DEVICE FOR HUMAN TOUCH," by Salvia, having
Attorney Docket No. IVS-684.PR, and assigned to the assignee of the
present application, which is incorporated herein by reference in
its entirety.
BACKGROUND
[0003] Conventional fingerprint sensing solutions are available and
deployed in consumer products, such as smartphones and other type
of mobile devices. Common fingerprint sensor technologies generally
rely on (1) a sensor and (2) a processing element. When the sensor
is turned on, the sensor can take or can direct the device to take
an image, which is digitized (e.g., level of brightness is encoded
into a digital format), and send the image to the processing
element. However, finger print sensors typically consume
substantial amount of power (e.g., hundreds of .mu.Watts to several
mWatts) and, therefore, may present a considerable drain on power
resources of the mobile device by rapidly draining the battery of
the mobile device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The accompanying drawings, which are incorporated in and
form a part of the Description of Embodiments, illustrate various
embodiments of the subject matter and, together with the
Description of Embodiments, serve to explain principles of the
subject matter discussed below. Unless specifically noted, the
drawings referred to in this Brief Description of Drawings should
be understood as not being drawn to scale. Herein, like items are
labeled with like item numbers.
[0005] FIG. 1 is a diagram illustrating a PMUT device having a
center pinned membrane, according to some embodiments.
[0006] FIG. 2 is a diagram illustrating an example of membrane
movement during activation of a PMUT device, according to some
embodiments.
[0007] FIG. 3 is a top view of the PMUT device of FIG. 1, according
to some embodiments.
[0008] FIG. 4 is a simulated map illustrating maximum vertical
displacement of the membrane of the PMUT device shown in FIGS. 1-3,
according to some embodiments.
[0009] FIG. 5 is a top view of an example PMUT device having a
circular shape, according to some embodiments.
[0010] FIG. 6 is a top view of an example PMUT device having a
hexagonal shape, according to some embodiments.
[0011] FIG. 7 illustrates an example array of circular-shaped PMUT
devices, according to some embodiments.
[0012] FIG. 8 illustrates an example array of square-shaped PMUT
devices, according to some embodiments.
[0013] FIG. 9 illustrates an example array of hexagonal-shaped PMUT
devices, according to some embodiments.
[0014] FIG. 10 illustrates an example pair of PMUT devices in a
PMUT array, with each PMUT having differing electrode patterning,
according to some embodiments.
[0015] FIGS. 11A, 11B, 11C, and 11D illustrate alternative examples
of interior support structures, according to various
embodiments.
[0016] FIG. 12 illustrates a PMUT array used in an ultrasonic
fingerprint sensing system, according to some embodiments.
[0017] FIG. 13 illustrates an integrated fingerprint sensor formed
by wafer bonding a CMOS logic wafer and a microelectromechanical
(MEMS) wafer defining PMUT devices, according to some
embodiments.
[0018] FIG. 14 illustrates an example ultrasonic transducer system
with phase delayed transmission, according to some embodiments.
[0019] FIG. 15 illustrates another example ultrasonic transducer
system with phase delayed transmission, according to some
embodiments.
[0020] FIG. 16 illustrates an example phase delay pattern for a
9.times.9 ultrasonic transducer block, according to some
embodiments.
[0021] FIG. 17 illustrates another example phase delay pattern for
a 9.times.9 ultrasonic transducer block, according to some
embodiments.
[0022] FIG. 18A illustrates an example of an operational
environment for sensing of human touch, according to some
embodiments.
[0023] FIG. 18B illustrates an example fingerprint sensor, in
accordance with various embodiments.
[0024] FIG. 19 illustrates example operation in a first phase of a
finger detection mode associated with a two-dimensional array of
ultrasonic transducers, according to some embodiments.
[0025] FIG. 20 illustrates an example duty-cycle timeline 2000 for
the first phase of the finger detection mode, according to an
embodiment.
[0026] FIG. 21 illustrates an example of thresholding for the first
phase of the finger detection mode, in accordance with various
embodiments.
[0027] FIG. 22 illustrates example operation in a second phase of a
finger detection mode associated with a two-dimensional array of
ultrasonic transducers, according to some embodiments.
[0028] FIG. 23 illustrates an example duty-cycle timeline 2300 for
the second phase of the finger detection mode, according to an
embodiment.
[0029] FIG. 24 illustrates an example of thresholding for the
second phase of the finger detection mode, in accordance with
various embodiments.
[0030] FIGS. 25A-D illustrate another example of thresholding for
the second phase of the finger detection mode, in accordance with
various embodiments.
[0031] FIGS. 26 through 28 illustrate flow diagrams of example
methods for operating a fingerprint sensor comprised of ultrasonic
transducers, according to various embodiments.
DESCRIPTION OF EMBODIMENTS
[0032] The following Description of Embodiments is merely provided
by way of example and not of limitation. Furthermore, there is no
intention to be bound by any expressed or implied theory presented
in the preceding background or in the following Description of
Embodiments.
[0033] Reference will now be made in detail to various embodiments
of the subject matter, examples of which are illustrated in the
accompanying drawings. While various embodiments are discussed
herein, it will be understood that they are not intended to limit
to these embodiments. On the contrary, the presented embodiments
are intended to cover alternatives, modifications and equivalents,
which may be included within the spirit and scope the various
embodiments as defined by the appended claims. Furthermore, in this
Description of Embodiments, numerous specific details are set forth
in order to provide a thorough understanding of embodiments of the
present subject matter. However, embodiments may be practiced
without these specific details. In other instances, well known
methods, procedures, components, and circuits have not been
described in detail as not to unnecessarily obscure aspects of the
described embodiments.
Notation and Nomenclature
[0034] Some portions of the detailed descriptions which follow are
presented in terms of procedures, logic blocks, processing and
other symbolic representations of operations on data within an
electrical device. These descriptions and representations are the
means used by those skilled in the data processing arts to most
effectively convey the substance of their work to others skilled in
the art. In the present application, a procedure, logic block,
process, or the like, is conceived to be one or more
self-consistent procedures or instructions leading to a desired
result. The procedures are those requiring physical manipulations
of physical quantities. Usually, although not necessarily, these
quantities take the form of acoustic (e.g., ultrasonic) signals
capable of being transmitted and received by an electronic device
and/or electrical or magnetic signals capable of being stored,
transferred, combined, compared, and otherwise manipulated in an
electrical device.
[0035] It should be borne in mind, however, that all of these and
similar terms are to be associated with the appropriate physical
quantities and are merely convenient labels applied to these
quantities. Unless specifically stated otherwise as apparent from
the following discussions, it is appreciated that throughout the
description of embodiments, discussions utilizing terms such as
"activating," "detecting," "determining," "capturing," "sensing,"
"generating," "imaging," "performing," "comparing," "updating,"
"transmitting," "entering," or the like, refer to the actions and
processes of an electronic device such as an electrical device.
[0036] Embodiments described herein may be discussed in the general
context of processor-executable instructions residing on some form
of non-transitory processor-readable medium, such as program
modules, executed by one or more computers or other devices.
Generally, program modules include routines, programs, objects,
components, data structures, etc., that perform particular tasks or
implement particular abstract data types. The functionality of the
program modules may be combined or distributed as desired in
various embodiments.
[0037] In the figures, a single block may be described as
performing a function or functions; however, in actual practice,
the function or functions performed by that block may be performed
in a single component or across multiple components, and/or may be
performed using hardware, using software, or using a combination of
hardware and software. To clearly illustrate this
interchangeability of hardware and software, various illustrative
components, blocks, modules, logic, circuits, and steps have been
described generally in terms of their functionality. Whether such
functionality is implemented as hardware or software depends upon
the particular application and design constraints imposed on the
overall system. Skilled artisans may implement the described
functionality in varying ways for each particular application, but
such implementation decisions should not be interpreted as causing
a departure from the scope of the present disclosure. Also, the
example fingerprint sensing system and/or mobile electronic device
described herein may include components other than those shown,
including well-known components.
[0038] Various techniques described herein may be implemented in
hardware, software, firmware, or any combination thereof, unless
specifically described as being implemented in a specific manner.
Any features described as modules or components may also be
implemented together in an integrated logic device or separately as
discrete but interoperable logic devices. If implemented in
software, the techniques may be realized at least in part by a
non-transitory processor-readable storage medium comprising
instructions that, when executed, perform one or more of the
methods described herein. The non-transitory processor-readable
data storage medium may form part of a computer program product,
which may include packaging materials.
[0039] The non-transitory processor-readable storage medium may
comprise random access memory (RAM) such as synchronous dynamic
random access memory (SDRAM), read only memory (ROM), non-volatile
random access memory (NVRAM), electrically erasable programmable
read-only memory (EEPROM), FLASH memory, other known storage media,
and the like. The techniques additionally, or alternatively, may be
realized at least in part by a processor-readable communication
medium that carries or communicates code in the form of
instructions or data structures and that can be accessed, read,
and/or executed by a computer or other processor.
[0040] Various embodiments described herein may be executed by one
or more processors, such as one or more motion processing units
(MPUs), sensor processing units (SPUs), host processor(s) or
core(s) thereof, digital signal processors (DSPs), general purpose
microprocessors, application specific integrated circuits (ASICs),
application specific instruction set processors (ASIPs), field
programmable gate arrays (FPGAs), a programmable logic controller
(PLC), a complex programmable logic device (CPLD), a discrete gate
or transistor logic, discrete hardware components, or any
combination thereof designed to perform the functions described
herein, or other equivalent integrated or discrete logic circuitry.
The term "processor," as used herein may refer to any of the
foregoing structures or any other structure suitable for
implementation of the techniques described herein. As it employed
in the subject specification, the term "processor" can refer to
substantially any computing processing unit or device comprising,
but not limited to comprising, single-core processors;
single-processors with software multithread execution capability;
multi-core processors; multi-core processors with software
multithread execution capability; multi-core processors with
hardware multithread technology; parallel platforms; and parallel
platforms with distributed shared memory. Moreover, processors can
exploit nano-scale architectures such as, but not limited to,
molecular and quantum-dot based transistors, switches and gates, in
order to optimize space usage or enhance performance of user
equipment. A processor may also be implemented as a combination of
computing processing units.
[0041] In addition, in some aspects, the functionality described
herein may be provided within dedicated software modules or
hardware modules configured as described herein. Also, the
techniques could be fully implemented in one or more circuits or
logic elements. A general purpose processor may be a
microprocessor, but in the alternative, the processor may be any
conventional processor, controller, microcontroller, or state
machine. A processor may also be implemented as a combination of
computing devices, e.g., a combination of an SPU/MPU and a
microprocessor, a plurality of microprocessors, one or more
microprocessors in conjunction with an SPU core, MPU core, or any
other such configuration.
Overview of Discussion
[0042] Discussion begins with a description of an example
piezoelectric micromachined ultrasonic transducer (PMUT), in
accordance with various embodiments. Example arrays including PMUT
devices are then described. Example operations of example arrays of
ultrasonic transducers (e.g., PMUT devices) are then further
described, including the use of multiple PMUT devices to form a
beam for capturing a pixel. Examples of a fingerprint sensor, and
operations pertaining to the use of a fingerprint sensor, are then
described.
[0043] Embodiments described herein relate to a method of operating
a two-dimensional array of ultrasonic transducers. When an
ultrasonic transducer, such as a PMUT device, transmits an
ultrasonic signal, the ultrasonic signal typically does not
transmit as a straight line. Rather, the ultrasonic signal will
transmit to a wider area. For instance, when traveling through a
transmission medium, the ultrasonic signal will diffract, thus
transmitting to a wide area.
[0044] Embodiments described herein provide fingerprint sensing
system including an array of ultrasonic transducers for sensing the
fingerprint. In order to accurately sense a fingerprint, it is
desirable to sense a high resolution image of the fingerprint.
Using multiple ultrasonic transducers, some of which are time
delayed with respect to other ultrasonic transducers, embodiments
described herein provide for focusing a transmit beam (e.g.,
forming a beam) of an ultrasonic signal to a desired point,
allowing for high resolution sensing of a fingerprint, or other
object. For instance, transmitting an ultrasonic signal from
multiple PMUTs, where some PMUTs transmit at a time delay relative
to other PMUTs, provides for focusing the ultrasonic beam to a
contact point of a fingerprint sensing system (e.g., a top of a
platen layer) for sensing a high resolution image of a pixel
associated with the transmitting PMUTs.
[0045] Embodiments described herein further provide for the
implementation of a finger detection mode for use with a
fingerprint sensor operating within an electronic device. In one
embodiment, the fingerprint sensor includes an array of PMUT
devices. The finger detection mode is operable to identify if a
finger interacts with a fingerprint sensor and allows for the
fingerprint sensor to operate in an always-on state, while reducing
power consumption of the fingerprint sensor. In the described
embodiments, the finger detection mode can operate in one or more
phases to detect whether a finger has interacted with a fingerprint
sensor. If it is determined that a finger has interacted with the
fingerprint sensor, the fingerprint sensor may be fully powered on
to capture a full image of the fingerprint for further processing.
Alternatively, if it is determined that something other than a
finger has interacted with the fingerprint sensor, the fingerprint
sensor may remain in a low power finger detection mode (e.g.,
always-on state).
Piezoelectric Micromachined Ultrasonic Transducer (PMUT)
[0046] Systems and methods disclosed herein, in one or more aspects
provide efficient structures for an acoustic transducer (e.g., a
piezoelectric micromachined actuated transducer or PMUT). One or
more embodiments are now described with reference to the drawings,
wherein like reference numerals are used to refer to like elements
throughout. In the following description, for purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of the various embodiments. It may
be evident, however, that the various embodiments can be practiced
without these specific details. In other instances, well-known
structures and devices are shown in block diagram form in order to
facilitate describing the embodiments in additional detail.
[0047] As used in this application, the term "or" is intended to
mean an inclusive "or" rather than an exclusive "or". That is,
unless specified otherwise, or clear from context, "X employs A or
B" is intended to mean any of the natural inclusive permutations.
That is, if X employs A; X employs B; or X employs both A and B,
then "X employs A or B" is satisfied under any of the foregoing
instances. In addition, the articles "a" and "an" as used in this
application and the appended claims should generally be construed
to mean "one or more" unless specified otherwise or clear from
context to be directed to a singular form. In addition, the word
"coupled" is used herein to mean direct or indirect electrical or
mechanical coupling. In addition, the word "example" is used herein
to mean serving as an example, instance, or illustration.
[0048] FIG. 1 is a diagram illustrating a PMUT device 100 having a
center pinned membrane, according to some embodiments. PMUT device
100 includes an interior pinned membrane 120 positioned over a
substrate 140 to define a cavity 130. In one embodiment, membrane
120 is attached both to a surrounding edge support 102 and interior
support 104. In one embodiment, edge support 102 is connected to an
electric potential. Edge support 102 and interior support 104 may
be made of electrically conducting materials, such as and without
limitation, aluminum, molybdenum, or titanium. Edge support 102 and
interior support 104 may also be made of dielectric materials, such
as silicon dioxide, silicon nitride or aluminum oxide that have
electrical connections on the sides or in vias through edge support
102 or interior support 104, electrically coupling lower electrode
106 to electrical wiring in substrate 140.
[0049] In one embodiment, both edge support 102 and interior
support 104 are attached to a substrate 140. In various
embodiments, substrate 140 may include at least one of, and without
limitation, silicon or silicon nitride. It should be appreciated
that substrate 140 may include electrical wirings and connection,
such as aluminum or copper. In one embodiment, substrate 140
includes a CMOS logic wafer bonded to edge support 102 and interior
support 104. In one embodiment, the membrane 120 comprises multiple
layers. In an example embodiment, the membrane 120 includes lower
electrode 106, piezoelectric layer 110, and upper electrode 108,
where lower electrode 106 and upper electrode 108 are coupled to
opposing sides of piezoelectric layer 110. As shown, lower
electrode 106 is coupled to a lower surface of piezoelectric layer
110 and upper electrode 108 is coupled to an upper surface of
piezoelectric layer 110. It should be appreciated that, in various
embodiments, PMUT device 100 is a microelectromechanical (MEMS)
device.
[0050] In one embodiment, membrane 120 also includes a mechanical
support layer 112 (e.g., stiffening layer) to mechanically stiffen
the layers. In various embodiments, mechanical support layer 112
may include at least one of, and without limitation, silicon,
silicon oxide, silicon nitride, aluminum, molybdenum, titanium,
etc. In one embodiment, PMUT device 100 also includes an acoustic
coupling layer 114 above membrane 120 for supporting transmission
of acoustic signals. It should be appreciated that acoustic
coupling layer can include air, liquid, gel-like materials, epoxy,
or other materials for supporting transmission of acoustic signals.
In one embodiment, PMUT device 100 also includes platen layer 116
above acoustic coupling layer 114 for containing acoustic coupling
layer 114 and providing a contact surface for a finger or other
sensed object with PMUT device 100. It should be appreciated that,
in various embodiments, acoustic coupling layer 114 provides a
contact surface, such that platen layer 116 is optional. Moreover,
it should be appreciated that acoustic coupling layer 114 and/or
platen layer 116 may be included with or used in conjunction with
multiple PMUT devices. For example, an array of PMUT devices may be
coupled with a single acoustic coupling layer 114 and/or platen
layer 116.
[0051] FIG. 2 is a diagram illustrating an example of membrane
movement during activation of PMUT device 100, according to some
embodiments. As illustrated with respect to FIG. 2, in operation,
responsive to an object proximate platen layer 116, the electrodes
106 and 108 deliver a high frequency electric charge to the
piezoelectric layer 110, causing those portions of the membrane 120
not pinned to the surrounding edge support 102 or interior support
104 to be displaced upward into the acoustic coupling layer 114.
This generates a pressure wave that can be used for signal probing
of the object. Return echoes can be detected as pressure waves
causing movement of the membrane, with compression of the
piezoelectric material in the membrane causing an electrical signal
proportional to amplitude of the pressure wave.
[0052] The described PMUT device 100 can be used with almost any
electrical device that converts a pressure wave into mechanical
vibrations and/or electrical signals. In one aspect, the PMUT
device 100 can comprise an acoustic sensing element (e.g., a
piezoelectric element) that generates and senses ultrasonic sound
waves. An object in a path of the generated sound waves can create
a disturbance (e.g., changes in frequency or phase, reflection
signal, echoes, etc.) that can then be sensed. The interference can
be analyzed to determine physical parameters such as (but not
limited to) distance, density and/or speed of the object. As an
example, the PMUT device 100 can be utilized in various
applications, such as, but not limited to, fingerprint or
physiologic sensors suitable for wireless devices, industrial
systems, automotive systems, robotics, telecommunications,
security, medical devices, etc. For example, the PMUT device 100
can be part of a sensor array comprising a plurality of ultrasonic
transducers deposited on a wafer, along with various logic, control
and communication electronics. A sensor array may comprise
homogenous or identical PMUT devices 100, or a number of different
or heterogonous device structures.
[0053] In various embodiments, the PMUT device 100 employs a
piezoelectric layer 110, comprised of materials such as, but not
limited to, Aluminum nitride (AlN), lead zirconate titanate (PZT),
quartz, polyvinylidene fluoride (PVDF), and/or zinc oxide, to
facilitate both acoustic signal production and sensing. The
piezoelectric layer 110 can generate electric charges under
mechanical stress and conversely experience a mechanical strain in
the presence of an electric field. For example, the piezoelectric
layer 110 can sense mechanical vibrations caused by an ultrasonic
signal and produce an electrical charge at the frequency (e.g.,
ultrasonic frequency) of the vibrations. Additionally, the
piezoelectric layer 110 can generate an ultrasonic wave by
vibrating in an oscillatory fashion that might be at the same
frequency (e.g., ultrasonic frequency) as an input current
generated by an alternating current (AC) voltage applied across the
piezoelectric layer 110. It should be appreciated that the
piezoelectric layer 110 can include almost any material (or
combination of materials) that exhibits piezoelectric properties,
such that the structure of the material does not have a center of
symmetry and a tensile or compressive stress applied to the
material alters the separation between positive and negative charge
sites in a cell causing a polarization at the surface of the
material. The polarization is directly proportional to the applied
stress and is direction dependent so that compressive and tensile
stresses results in electric fields of opposite polarizations.
[0054] Further, the PMUT device 100 comprises electrodes 106 and
108 that supply and/or collect the electrical charge to/from the
piezoelectric layer 110. It should be appreciated that electrodes
106 and 108 can be continuous and/or patterned electrodes (e.g., in
a continuous layer and/or a patterned layer). For example, as
illustrated, electrode 106 is a patterned electrode and electrode
108 is a continuous electrode. As an example, electrodes 106 and
108 can be comprised of almost any metal layers, such as, but not
limited to, Aluminum (Al)/Titanium (Ti), Molybdenum (Mo), etc.,
which are coupled with and on opposing sides of the piezoelectric
layer 110. In one embodiment, PMUT device also includes a third
electrode, as illustrated in FIG. 10 and described below.
[0055] According to an embodiment, the acoustic impedance of
acoustic coupling layer 114 is selected to be similar to the
acoustic impedance of the platen layer 116, such that the acoustic
wave is efficiently propagated to/from the membrane 120 through
acoustic coupling layer 114 and platen layer 116. As an example,
the platen layer 116 can comprise various materials having an
acoustic impedance in the range between 0.8 to 4 MRayl, such as,
but not limited to, plastic, resin, rubber, Teflon, epoxy, etc. In
another example, the platen layer 116 can comprise various
materials having a high acoustic impedance (e.g., an acoustic
impendence greater than 10 MiRayl), such as, but not limited to,
glass, aluminum-based alloys, sapphire, etc. Typically, the platen
layer 116 can be selected based on an application of the sensor.
For instance, in fingerprinting applications, platen layer 116 can
have an acoustic impedance that matches (e.g., exactly or
approximately) the acoustic impedance of human skin (e.g.,
1.6.times.10.sup.6 Rayl). Further, in one aspect, the platen layer
116 can further include a thin layer of anti-scratch material. In
various embodiments, the anti-scratch layer of the platen layer 116
is less than the wavelength of the acoustic wave that is to be
generated and/or sensed to provide minimum interference during
propagation of the acoustic wave. As an example, the anti-scratch
layer can comprise various hard and scratch-resistant materials
(e.g., having a Mohs hardness of over 7 on the Mohs scale), such
as, but not limited to sapphire, glass, MN, Titanium nitride (TiN),
Silicon carbide (SiC), diamond, etc. As an example, PMUT device 100
can operate at 20 MHz and accordingly, the wavelength of the
acoustic wave propagating through the acoustic coupling layer 114
and platen layer 116 can be 70-150 microns. In this example
scenario, insertion loss can be reduced and acoustic wave
propagation efficiency can be improved by utilizing an anti-scratch
layer having a thickness of 1 micron and the platen layer 116 as a
whole having a thickness of 1-2 millimeters. It is noted that the
term "anti-scratch material" as used herein relates to a material
that is resistant to scratches and/or scratch-proof and provides
substantial protection against scratch marks.
[0056] In accordance with various embodiments, the PMUT device 100
can include metal layers (e.g., Aluminum (A1)/Titanium (Ti),
Molybdenum (Mo), etc.) patterned to form electrode 106 in
particular shapes (e.g., ring, circle, square, octagon, hexagon,
etc.) that are defined in-plane with the membrane 120. Electrodes
can be placed at a maximum strain area of the membrane 120 or
placed at close to either or both the surrounding edge support 102
and interior support 104. Furthermore, in one example, electrode
108 can be formed as a continuous layer providing a ground plane in
contact with mechanical support layer 112, which can be formed from
silicon or other suitable mechanical stiffening material. In still
other embodiments, the electrode 106 can be routed along the
interior support 104, advantageously reducing parasitic capacitance
as compared to routing along the edge support 102.
[0057] For example, when actuation voltage is applied to the
electrodes, the membrane 120 will deform and move out of plane. The
motion then pushes the acoustic coupling layer 114 it is in contact
with and an acoustic (ultrasonic) wave is generated. Oftentimes,
vacuum is present inside the cavity 130 and therefore damping
contributed from the media within the cavity 130 can be ignored.
However, the acoustic coupling layer 114 on the other side of the
membrane 120 can substantially change the damping of the PMUT
device 100. For example, a quality factor greater than 20 can be
observed when the PMUT device 100 is operating in air with
atmosphere pressure (e.g., acoustic coupling layer 114 is air) and
can decrease lower than 2 if the PMUT device 100 is operating in
water (e.g., acoustic coupling layer 114 is water).
[0058] FIG. 3 is a top view of the PMUT device 100 of FIG. 1 having
a substantially square shape, which corresponds in part to a cross
section along dotted line 101 in FIG. 3. Layout of surrounding edge
support 102, interior support 104, and lower electrode 106 are
illustrated, with other continuous layers not shown. It should be
appreciated that the term "substantially" in "substantially square
shape" is intended to convey that a PMUT device 100 is generally
square-shaped, with allowances for variations due to manufacturing
processes and tolerances, and that slight deviation from a square
shape (e.g., rounded corners, slightly wavering lines, deviations
from perfectly orthogonal corners or intersections, etc.) may be
present in a manufactured device. While a generally square
arrangement PMUT device is shown, alternative embodiments including
rectangular, hexagon, octagonal, circular, or elliptical are
contemplated. In other embodiments, more complex electrode or PMUT
device shapes can be used, including irregular and non-symmetric
layouts such as chevrons or pentagons for edge support and
electrodes.
[0059] FIG. 4 is a simulated topographic map 400 illustrating
maximum vertical displacement of the membrane 120 of the PMUT
device 100 shown in FIGS. 1-3. As indicated, maximum displacement
generally occurs along a center axis of the lower electrode, with
corner regions having the greatest displacement. As with the other
figures, FIG. 4 is not drawn to scale with the vertical
displacement exaggerated for illustrative purposes, and the maximum
vertical displacement is a fraction of the horizontal surface area
comprising the PMUT device 100. In an example PMUT device 100,
maximum vertical displacement may be measured in nanometers, while
surface area of an individual PMUT device 100 may be measured in
square microns.
[0060] FIG. 5 is a top view of another example of the PMUT device
100 of FIG. 1 having a substantially circular shape, which
corresponds in part to a cross section along dotted line 101 in
FIG. 5. Layout of surrounding edge support 102, interior support
104, and lower electrode 106 are illustrated, with other continuous
layers not shown. It should be appreciated that the term
"substantially" in "substantially circular shape" is intended to
convey that a PMUT device 100 is generally circle-shaped, with
allowances for variations due to manufacturing processes and
tolerances, and that slight deviation from a circle shape (e.g.,
slight deviations on radial distance from center, etc.) may be
present in a manufactured device.
[0061] FIG. 6 is a top view of another example of the PMUT device
100 of FIG. 1 having a substantially hexagonal shape, which
corresponds in part to a cross section along dotted line 101 in
FIG. 6. Layout of surrounding edge support 102, interior support
104, and lower electrode 106 are illustrated, with other continuous
layers not shown. It should be appreciated that the term
"substantially" in "substantially hexagonal shape" is intended to
convey that a PMUT device 100 is generally hexagon-shaped, with
allowances for variations due to manufacturing processes and
tolerances, and that slight deviation from a hexagon shape (e.g.,
rounded corners, slightly wavering lines, deviations from perfectly
orthogonal corners or intersections, etc.) may be present in a
manufactured device.
[0062] FIG. 7 illustrates an example two-dimensional array 700 of
circular-shaped PMUT devices 701 formed from PMUT devices having a
substantially circular shape similar to that discussed in
conjunction with FIGS. 1, 2 and 5. Layout of circular surrounding
edge support 702, interior support 704, and annular or ring shaped
lower electrode 706 surrounding the interior support 704 are
illustrated, while other continuous layers are not shown for
clarity. As illustrated, array 700 includes columns of
circular-shaped PMUT devices 701 that are offset. It should be
appreciated that the circular-shaped PMUT devices 701 may be closer
together, such that edges of the columns of circular-shaped PMUT
devices 701 overlap. Moreover, it should be appreciated that
circular-shaped PMUT devices 701 may contact each other. In various
embodiments, adjacent circular-shaped PMUT devices 701 are
electrically isolated. In other embodiments, groups of adjacent
circular-shaped PMUT devices 701 are electrically connected, where
the groups of adjacent circular-shaped PMUT devices 701 are
electrically isolated.
[0063] FIG. 8 illustrates an example two-dimensional array 800 of
square-shaped PMUT devices 801 formed from PMUT devices having a
substantially square shape similar to that discussed in conjunction
with FIGS. 1, 2 and 3. Layout of square surrounding edge support
802, interior support 804, and square-shaped lower electrode 806
surrounding the interior support 804 are illustrated, while other
continuous layers are not shown for clarity. As illustrated, array
800 includes columns of square-shaped PMUT devices 801 that are in
rows and columns. It should be appreciated that rows or columns of
the square-shaped PMUT devices 801 may be offset. Moreover, it
should be appreciated that square-shaped PMUT devices 801 may
contact each other or be spaced apart. In various embodiments,
adjacent square-shaped PMUT devices 801 are electrically isolated.
In other embodiments, groups of adjacent square-shaped PMUT devices
801 are electrically connected, where the groups of adjacent
square-shaped PMUT devices 801 are electrically isolated.
[0064] FIG. 9 illustrates an example two-dimensional array 900 of
hexagon-shaped PMUT devices 901 formed from PMUT devices having a
substantially hexagon shape similar to that discussed in
conjunction with FIGS. 1, 2 and 6. Layout of hexagon-shaped
surrounding edge support 902, interior support 904, and
hexagon-shaped lower electrode 906 surrounding the interior support
904 are illustrated, while other continuous layers are not shown
for clarity. It should be appreciated that rows or columns of the
hexagon-shaped PMUT devices 901 may be offset. Moreover, it should
be appreciated that hexagon-shaped PMUT devices 901 may contact
each other or be spaced apart. In various embodiments, adjacent
hexagon-shaped PMUT devices 901 are electrically isolated. In other
embodiments, groups of adjacent hexagon-shaped PMUT devices 901 are
electrically connected, where the groups of adjacent hexagon-shaped
PMUT devices 901 are electrically isolated. While FIGS. 7, 8 and 9
illustrate example layouts of PMUT devices having different shapes,
it should be appreciated that many different layouts are available.
Moreover, in accordance with various embodiments, arrays of PMUT
devices are included within a MEMS layer.
[0065] In operation, during transmission, selected sets of PMUT
devices in the two-dimensional array can transmit an acoustic
signal (e.g., a short ultrasonic pulse) and during sensing, the set
of active PMUT devices in the two-dimensional array can detect an
interference of the acoustic signal with an object (in the path of
the acoustic wave). The received interference signal (e.g.,
generated based on reflections, echoes, etc. of the acoustic signal
from the object) can then be analyzed. As an example, an image of
the object, a distance of the object from the sensing component, a
density of the object, a motion of the object, etc., can all be
determined based on comparing a frequency and/or phase of the
interference signal with a frequency and/or phase of the acoustic
signal. Moreover, results generated can be further analyzed or
presented to a user via a display device (not shown).
[0066] FIG. 10 illustrates a pair of example PMUT devices 1000 in a
PMUT array, with each PMUT sharing at least one common edge support
1002. As illustrated, the PMUT devices have two sets of independent
lower electrode labeled as 1006 and 1026. These differing electrode
patterns enable antiphase operation of the PMUT devices 1000, and
increase flexibility of device operation. In one embodiment, the
pair of PMUTs may be identical, but the two electrodes could drive
different parts of the same PMUT antiphase (one contracting, and
one extending), such that the PMUT displacement becomes larger.
While other continuous layers are not shown for clarity, each PMUT
also includes an upper electrode (e.g., upper electrode 108 of FIG.
1). Accordingly, in various embodiments, a PMUT device may include
at least three electrodes.
[0067] FIGS. 11A, 11B, 11C, and 11D illustrate alternative examples
of interior support structures, in accordance with various
embodiments. Interior supports structures may also be referred to
as "pinning structures," as they operate to pin the membrane to the
substrate. It should be appreciated that interior support
structures may be positioned anywhere within a cavity of a PMUT
device, and may have any type of shape (or variety of shapes), and
that there may be more than one interior support structure within a
PMUT device. While FIGS. 11A, 11B, 11C, and 11D illustrate
alternative examples of interior support structures, it should be
appreciated that these examples are for illustrative purposes, and
are not intended to limit the number, position, or type of interior
support structures of PMUT devices.
[0068] For example, interior supports structures do not have to be
centrally located with a PMUT device area, but can be non-centrally
positioned within the cavity. As illustrated in FIG. 11A, interior
support 1104a is positioned in a non-central, off-axis position
with respect to edge support 1102. In other embodiments such as
seen in FIG. 11B, multiple interior supports 1104b can be used. In
this embodiment, one interior support is centrally located with
respect to edge support 1102, while the multiple, differently
shaped and sized interior supports surround the centrally located
support. In still other embodiments, such as seen with respect to
FIGS. 11C and 11D, the interior supports (respectively 1104c and
1104d) can contact a common edge support 1102. In the embodiment
illustrated in FIG. 11D, the interior supports 1104d can
effectively divide the PMUT device into subpixels. This would
allow, for example, activation of smaller areas to generate high
frequency ultrasonic waves, and sensing a returning ultrasonic echo
with larger areas of the PMUT device. It will be appreciated that
the individual pinning structures can be combined into arrays.
[0069] FIG. 12 illustrates an embodiment of a PMUT array used in an
ultrasonic fingerprint sensing system 1250. The fingerprint sensing
system 1250 can include a platen 1216 onto which a human finger
1252 may make contact. Ultrasonic signals are generated and
received by a PMUT device array 1200, and travel back and forth
through acoustic coupling layer 1214 and platen 1216. Signal
analysis is conducted using processing logic module 1240 (e.g.,
control logic) directly attached (via wafer bonding or other
suitable techniques) to the PMUT device array 1200. It will be
appreciated that the size of platen 1216 and the other elements
illustrated in FIG. 12 may be much larger (e.g., the size of a
handprint) or much smaller (e.g., just a fingertip) than as shown
in the illustration, depending on the particular application.
[0070] In this example for fingerprinting applications, the human
finger 1252 and the processing logic module 1240 can determine,
based on a difference in interference of the acoustic signal with
valleys and/or ridges of the skin on the finger, an image depicting
epi-dermis and/or dermis layers of the finger. Further, the
processing logic module 1240 can compare the image with a set of
known fingerprint images to facilitate identification and/or
authentication. Moreover, in one example, if a match (or
substantial match) is found, the identity of user can be verified.
In another example, if a match (or substantial match) is found, a
command/operation can be performed based on an authorization rights
assigned to the identified user. In yet another example, the
identified user can be granted access to a physical location and/or
network/computer resources (e.g., documents, files, applications,
etc.)
[0071] In another example, for finger-based applications, the
movement of the finger can be used for cursor tracking/movement
applications. In such embodiments, a pointer or cursor on a display
screen can be moved in response to finger movement. It is noted
that processing logic module 1240 can include or be connected to
one or more processors configured to confer at least in part the
functionality of system 1250. To that end, the one or more
processors can execute code instructions stored in memory, for
example, volatile memory and/or nonvolatile memory.
[0072] FIG. 13 illustrates an integrated fingerprint sensor 1300
formed by wafer bonding a CMOS logic wafer and a MEMS wafer
defining PMUT devices, according to some embodiments. FIG. 13
illustrates in partial cross section one embodiment of an
integrated fingerprint sensor formed by wafer bonding a substrate
1340 CMOS logic wafer and a MEMS wafer defining PMUT devices having
a common edge support 1302 and separate interior support 1304. For
example, the MEMS wafer may be bonded to the CMOS logic wafer using
aluminum and germanium eutectic alloys, as described in U.S. Pat.
No. 7,442,570. PMUT device 1300 has an interior pinned membrane
1320 formed over a cavity 1330. The membrane 1320 is attached both
to a surrounding edge support 1302 and interior support 1304. The
membrane 1320 is formed from multiple layers.
Example Operation of a Two-Dimensional Array of Ultrasonic
Transducers
[0073] Systems and methods disclosed herein, in one or more aspects
provide for the operation of a two-dimensional array of ultrasonic
transducers (e.g., an array of piezoelectric micromachined actuated
transducers or PMUTs). One or more embodiments are now described
with reference to the drawings, wherein like reference numerals are
used to refer to like elements throughout. In the following
description, for purposes of explanation, numerous specific details
are set forth in order to provide a thorough understanding of the
various embodiments. It may be evident, however, that the various
embodiments can be practiced without these specific details. In
other instances, well-known structures and devices are shown in
block diagram form in order to facilitate describing the
embodiments in additional detail.
[0074] FIG. 14 illustrates an example ultrasonic transducer system
1400 with phase delayed transmission, according to some
embodiments. As illustrated, FIG. 14 shows ultrasonic beam
transmission and reception using a one-dimensional, five-element,
ultrasonic transducer system 1400 having phase delayed inputs 1410.
In various embodiments, ultrasonic transducer system 1400 is
comprised of PMUT devices having a center pinned membrane (e.g.,
PMUT device 100 of FIG. 1).
[0075] As illustrated, ultrasonic transducer system 1400 includes
five ultrasonic transducers 1402 including a piezoelectric material
and activating electrodes that are covered with a continuous
stiffening layer 1404 (e.g., a mechanical support layer).
Stiffening layer 1404 contacts acoustic coupling layer 1406, and in
turn is covered by a platen layer 1408. In various embodiments, the
stiffening layer 1404 can be silicon, and the platen layer 1408
formed from metal, glass, sapphire, or polycarbonate or similar
durable plastic. The intermediately positioned acoustic coupling
layer 1406 can be formed from a plastic or gel such as
polydimethylsiloxane (PDMS), epoxy, or other material. In one
embodiment, the material of acoustic coupling layer 1406 has an
acoustic impedance selected to be between the acoustic impedance of
layers 1404 and 1408. In one embodiment, the material of acoustic
coupling layer 1406 has an acoustic impedance selected to be close
the acoustic impedance of platen layer 1408, to reduce unwanted
acoustic reflections and improve ultrasonic beam transmission and
sensing. However, alternative material stacks to the one shown in
FIG. 14 may be used and certain layers may be omitted, provided the
medium through which transmission occurs passes signals in a
predictable way.
[0076] In operation, and as illustrated in FIG. 14, the ultrasonic
transducers 1402 labelled with an "x" are triggered to emit
ultrasonic waves at an initial time. At a second time, (e.g., 1-100
nanoseconds later), the ultrasonic transducers 1402 labelled with a
"y" are triggered. At a third time (e.g., 1-100 nanoseconds after
the second time) the ultrasonic transducer 1402 labelled with a "z"
is triggered. The ultrasonic waves transmitted at different times
cause interference with each other, effectively resulting in a
single high intensity beam 1420 that exits the platen layer 1408,
contacts objects, such as a finger (not shown), that contact the
platen layer 1408, and is in part reflected back to the ultrasonic
transducers. In one embodiment, the ultrasonic transducers 1402 are
switched from a transmission mode to a reception mode, allowing the
"z" ultrasonic transducer to detect any reflected signals. In other
words, the phase delay pattern of the ultrasonic transducers 1402
is symmetric about the focal point where high intensity beam 1420
exits platen layer 1408.
[0077] It should be appreciated that an ultrasonic transducer 1402
of ultrasonic transducer system 1400 may be used to transmit and/or
receive an ultrasonic signal, and that the illustrated embodiment
is a non-limiting example. The received signal 1422 (e.g.,
generated based on reflections, echoes, etc. of the acoustic signal
from an object contacting or near the platen layer 1408) can then
be analyzed. As an example, an image of the object, a distance of
the object from the sensing component, acoustic impedance of the
object, a motion of the object, etc., can all be determined based
on comparing a frequency, amplitude and/or phase of the received
interference signal with a frequency, amplitude and/or phase of the
transmitted acoustic signal. Moreover, results generated can be
further analyzed or presented to a user via a display device (not
shown).
[0078] FIG. 15 illustrates another example ultrasonic transducer
system 1500 with phase delayed transmission, according to some
embodiments. As illustrated, FIG. 15 shows ultrasonic beam
transmission and reception using a virtual block of
two-dimensional, 24-element, ultrasonic transducers that form a
subset of a 40-element ultrasonic transducer system 1500 having
phase delayed inputs. In operation, an array position 1530
(represented by the dotted line), also referred to herein as a
virtual block, includes columns 1520, 1522 and 1524 of ultrasonic
transducers 1502. At an initial time, columns 1520 and 1524 of
array position 1530 are triggered to emit ultrasonic waves at an
initial time. At a second time (e.g., several nanoseconds later),
column 1522 of array position 1530 is triggered. The ultrasonic
waves interfere with each other, substantially resulting in
emission of a high intensity ultrasonic wave centered on column
1522. In one embodiment, the ultrasonic transducers 1502 in columns
1520 and 1524 are switched off, while column 1522 is switched from
a transmission mode to a reception mode, allowing detection of any
reflected signals.
[0079] In one embodiment, after the activation of ultrasonic
transducers 1502 of array position 1530, ultrasonic transducers
1502 of another array position 1532, comprised of columns 1524,
1526, and 1528 of ultrasonic transducers 1502 are triggered in a
manner similar to that described in the foregoing description of
array position 1530. In one embodiment, ultrasonic transducers 1502
of another array position 1532 are activated after a detection of a
reflected ultrasonic signal at column 1522 of array position 1530.
It should be appreciated that while movement of the array position
by two columns of ultrasonic transducers is illustrated, movement
by one, three, or more columns rightward or leftward is
contemplated, as is movement by one or more rows, or by movement by
both some determined number of rows and columns. In various
embodiments, successive array positions can be either overlapping
in part, or can be distinct. In some embodiments the size of array
positions can be varied. In various embodiments, the number of
ultrasonic transducers 1502 of an array position for emitting
ultrasonic waves can be larger than the number of ultrasonic
transducers 1502 of an array position for ultrasonic reception. In
still other embodiments, array positions can be square,
rectangular, ellipsoidal, circular, or more complex shapes such as
crosses.
[0080] FIG. 16 illustrates an example phase delay pattern for
ultrasonic signal transmission of a 9.times.9 ultrasonic transducer
block 1600 of a two-dimensional array of ultrasonic transducers,
according to some embodiments. As illustrated in FIG. 16, each
number in the ultrasonic transducer array is equivalent to the
nanosecond delay used during operation, and an empty element (e.g.,
no number) in the ultrasonic transducer block 1600 means that an
ultrasonic transducer is not activated for signal transmission
during operation. In various embodiments, ultrasonic wave amplitude
can be the same or similar for each activated ultrasonic
transducer, or can be selectively increased or decreased relative
to other ultrasonic transducers. In the illustrated pattern,
initial ultrasonic transducer activation is limited to corners of
ultrasonic transducer block 1600, followed 10 nanoseconds later by
a rough ring around the edges of ultrasonic transducer block 1600.
After 23 nanoseconds, an interior ring of ultrasonic transducers is
activated. Together, the twenty-four activated ultrasonic
transducers generate an ultrasonic beam centered on the ultrasonic
transducer block 1600. In other words, the phase delay pattern of
ultrasonic transducer block 1600 is symmetric about the focal point
where a high intensity beam contacts an object.
[0081] It should be appreciated that different ultrasonic
transducers of ultrasonic transducer block 1600 may be activated
for receipt of reflected ultrasonic signals. For example, the
center 3.times.3 ultrasonic transducers of ultrasonic transducer
block 1600 may be activated to receive the reflected ultrasonic
signals. In another example, the ultrasonic transducers used to
transmit the ultrasonic signal are also used to receive the
reflected ultrasonic signal. In another example, the ultrasonic
transducers used to receive the reflected ultrasonic signals
include at least one of the ultrasonic transducers also used to
transmit the ultrasonic signals.
[0082] FIG. 17 illustrates another example phase delay pattern for
a 9.times.9 ultrasonic transducer block 1700, according to some
embodiments. As illustrated in FIG. 17, the example phase delay
pattern utilizes equidistant spacing of transmitting ultrasonic
transducers. As illustrated in FIG. 16, each number in the
ultrasonic transducer array is equivalent to the nanosecond delay
used during operation, and an empty element (e.g., no number) in
the ultrasonic transducer block 1700 means that an ultrasonic
transducer is not activated for signal transmission during
operation. In the illustrated embodiment, the initial ultrasonic
transducer activation is limited to corners of ultrasonic
transducer block 1700, followed 11 nanoseconds later by a rough
ring around the edges of ultrasonic transducer block 1700. After 22
nanoseconds, an interior ring of ultrasonic transducers is
activated. The illustrated embodiment utilizes equidistant spacing
of the transmitting ultrasonic transducers to reduce issues with
crosstalk and heating, wherein each activated ultrasonic
transducers is surrounded by un-activated ultrasonic transducers.
Together, the twenty-four activated ultrasonic transducers generate
an ultrasonic beam centered on the ultrasonic transducer block
1700.
Example Operation of a Fingerprint Sensor Comprised of Ultrasonic
Transducers
[0083] Various embodiments described herein provide a finger
detection mode for identifying if a finger has been placed on a
fingerprint sensor. If a finger's presence is detected on the
fingerprint sensor, in one embodiment, the system will exit the
finger detection mode in order capture the fingerprint image.
Embodiments described herein provide for a finger detection mode
that minimizes the number of false rejects and minimizes power
consumption of the fingerprint sensor. In finger detection mode, a
false reject is defined as failing to recognize that a finger is
present on the sensor when a finger is in fact interacting with the
fingerprint sensor. False rejects are viewed as catastrophic
failures in finger detection mode, because they could prevent a
user from turning on the device. False accepts (e.g., the
fingerprint sensor detects a finger when no finger is present)
increase the average power consumption of the system because the
fingerprint sensor and associated processor activate to do a full
fingerprint scan even though no finger is present. As a result,
minimizing false accepts is related to minimizing power
consumption.
[0084] The disclosure recognizes and addresses, in at least certain
embodiments, the issue of power consumption and lack of a power
efficient always-on approach to sensing and analyzing human touch
at a device. To that end, embodiments described herein permit or
otherwise facilitate sensing of human touch that can be performed
continually or nearly continually by separating a low-power
detection stage from a full-power analysis stage. The detection
stage is implemented continually or nearly continually and causes
system circuitry to perform analysis of the human touch after the
low-power detection stage has confirmed the human touch.
[0085] Implementation of the low-power detection stage permits
removal of physical actuation device (e.g., buttons or the like)
while maintaining low power consumption. Absence of a physical
actuation device does not hinder low-power consumption and does
simplify user-device interaction when sensing human touch. While
embodiments of the disclosure are illustrated with reference to a
mobile electronic device, the embodiments are not limited in this
respect and the embodiments can be applied to any device (mobile or
otherwise) having a surface that is sensitive to touch and permits
or otherwise facilitates control of the device by an end-user. Such
a touch-sensitive surface can embody or can constitute, for
example, a fingerprint sensor. Mobile devices can be embodied in or
can include consumer electronics devices (e.g., smartphones,
portable gaming devices); vehicular devices (such as navigation
and/or entertainment system device); medical devices; keys (e.g.,
for locking and gaining access to buildings, storage receptacles,
cars, etc.); and the like.
[0086] When compared to conventional technologies, embodiments
described herein can provide numerous improvements. For example,
splitting the sensing of human touch into a low power, always-on
detection stage and a triggered, full-power analysis stage permits
sensing human touch continuously or nearly continuously, without
causing battery drainage or other inefficiencies. Therefore,
embodiments described herein permit removal of physical actuation
triggers that are present in typical consumer electronics products,
thus simplifying user-device interaction while sensing human touch.
More specifically, rather than asking an end-user to provide some
activation trigger (such as pressing a button) before the
fingerprint sensing is turned on, for example, the low-power
detection stage of the disclosure is implemented continually and
trigger analysis when human touch is detected. For another example,
in view of the removal of physical actuation device for human
sensing, embodiments of the disclosure provide greater flexibility
of product design. In one embodiment, a touch-screen display device
can be implemented with a uniform (and fixed) screen without a
button press section. As such, the touch-screen display device can
provide always-on sensing of human touch while providing larger
viewing area and lower manufacturing cost for a product
incorporating embodiments of this disclosure. In contrast,
conventional sensor technology can operate one-hundred percent of
the time if a physical trigger is not desired, which would impose
prohibitive power consumption demands.
[0087] With reference to the drawings, FIG. 18A illustrates an
example of an operational environment 1800 for sensing of human
touch in accordance with one or more embodiments of the disclosure.
As illustrated, a device 1810 includes a fingerprint sensor 1815 or
other type of surface sensitive to touch. In one embodiment,
fingerprint sensor 1815 is disposed beneath a touch-screen display
device of device 1810. In another embodiment, fingerprint sensor
1815 is disposed adjacent or close to a touch-screen display device
of device 1810. In another embodiment, fingerprint sensor 1815 is
comprised within a touch-screen display device of device 1810. It
should be appreciated that device 1810 includes a fingerprint
sensor 1815 for sensing a fingerprint of a finger interacting with
device 1810.
[0088] In one embodiment, a human finger (represented by a hand
1820), can touch or interact with a specific area of device 1810
proximate fingerprint sensor 1815. In various embodiments,
fingerprint sensor 1815 can be hard and need not include movable
parts, such as a sensor button configured to detect human touch or
otherwise cause the device 1810 to respond to human touch. The
device 1810 can include circuitry that can operate in response to
touch (human or otherwise) of the touch-screen display device
and/or fingerprint sensor 1815 (or, in some embodiments, the other
type of touch sensitive surface).
[0089] In accordance with the described embodiments, device 1810
includes always-on circuitry 1830 and system circuitry 1840. It
should be appreciated that components of always-on circuitry 1830
and system circuitry 1840 might be disposed within the same
componentry, and are conceptually distinguished herein such that
always-on circuity 1830 includes components that are always-on, or
mostly always-on, and system circuitry 1840 includes components
that are powered off until they are powered on, for example, in
response to an activation signal received from always-on circuitry
1830. For example, such circuitry can be operatively coupled (e.g.,
electrically coupled, communicative coupled, etc.) via a bus
architecture 1835 (or bus 1835) or conductive conduits configured
to permit the exchange of signals between the always-on circuitry
1830 and the system circuitry 1840. In some embodiments, a printed
circuit board (PCB) placed behind a touch-screen display device can
include the always-on circuitry 1830, the system circuitry 1840,
and the bus 1835. In one embodiment, the always-on circuitry 1830
and the system circuitry 1840 can be configured or otherwise
arranged in a single semiconductor die. In another embodiment, the
always-on circuitry 1830 can be configured or otherwise arranged in
a first semiconductor die and the system circuitry 1840 can be
configured or otherwise arranged in a second semiconductor die. In
addition, in some embodiments, the bus 1835 can be embodied in or
can include a dedicated conducting wire or a dedicated data line
that connects the always-on circuitry 1830 and the system circuitry
1840.
[0090] The always-on circuitry 1830 can operate as sensor for human
touch and the system circuitry 1840, or a portion thereof, can
permit or otherwise facilitate analysis of the human touch. As
described herein, always-on circuitry 1830 includes fingerprint
sensor 1815. For example, responsive to capturing an image of a
fingerprint, fingerprint sensor 1815 can transmit the captured
image to system circuitry for analysis.
[0091] The analysis can include fingerprint recognition or other
types of biometric evaluations. The always-on circuitry 1830 can be
energized or otherwise power-on continuously or nearly continuously
and can be configured to monitor touch of fingerprint sensor 1815.
In addition, in response to human touch (e.g., touch by a human
finger or other human body part), the always-on circuitry 1830 can
be further configured to trigger detection and/or another type of
analysis of elements of the human touch or a human body associated
therewith. To at least that end, the always-on circuitry 1830 can
be configured to implement a first phase of a finger detection mode
(also referred to as FDMA).
[0092] FIG. 18B illustrates an example fingerprint sensor 1815, in
accordance with various embodiments. In one embodiment, fingerprint
sensor 1815 includes an array 1850 of ultrasonic transducers (e.g.,
PMUT devices), a processor 1860, and a memory 1870. In various
embodiments, processor 1860 performs certain operations in
accordance with instructions stored within memory 1870. It should
be appreciated that components of fingerprint sensor 1815 are
examples, and that certain components, such as processor 1860
and/or memory 1870 may not be located within fingerprint sensor
1815. For example, always-on circuitry 1830 or system circuitry
1840 may include a processor and/or memory for performing certain
operations.
[0093] In one embodiment, fingerprint sensor 1815 includes
processor 1860 for performing the pixel capture. In other
embodiments, processor 1860 can perform thresholding to determine
whether an object has interacted with fingerprint sensor 1815. In
other embodiments, processor 1860 can analyze captured pixels and
determine whether the object is a finger. In other embodiments,
processor 1860 can capture an image of the fingerprint and forward
it to a processor of system circuitry 1840 for further
analysis.
[0094] While the embodiment of FIG. 18B includes processor 1860 and
memory 1870, as described above, it should be appreciated that
various functions of processor 1860 and memory 1870 may reside in
other components of device 1810 (e.g., within always-on circuitry
1830 or system circuitry 1840). Moreover, it should be appreciated
that processor 1860 may be any type of processor for performing any
portion of the described functionality (e.g., custom digital
logic).
[0095] In various embodiments, a power supply can energize at least
a portion of the system circuitry 1840 according with trigger
signaling (or other type of control signal) provided (e.g.,
generated and transmitted) by the always-on circuitry 1830. For
example, system circuitry 1840 can include a power controller that
can receive trigger signaling (e.g., a control instruction) and, in
response, can energize at least one processor of the system
circuitry 1840 from a power-save state to a full-power state. The
at least one processor that transitions from the power-save state
to the full power state can execute one or more analyses in order
to analyze features (e.g., fingerprints) of an image of a
fingerprint from the fingerprint sensor 1815 that triggered the
trigger signaling. In various embodiments, the analysis of the
image of a fingerprint can include computer-accessible instruction
(e.g., computer-readable instructions and/or computer-executable
instructions) that in response to execution by a processor can
permit or otherwise facilitate the device 1810 to implement a
defined algorithm (or process) for fingerprint identification or
analysis.
[0096] In various embodiments, fingerprint sensor 1815 can include
ultrasonic transducers (e.g., PMUTs or capacitive micromachined
ultrasonic transducers (CMUTs)) able to generate and detect
pressure waves. Examples of PMUT devices and arrays of PMUT devices
are described in accordance with FIGS. 1-17 above. In embodiments,
a device 1810 includes fingerprint sensor 1815 comprised of an
array of PMUT devices that can facilitate ultrasonic signal
generation and sensing (transducer). For example, fingerprint
sensor 1815 can include a silicon wafer having a two-dimensional
(or one-dimensional) array of ultrasonic transducers.
[0097] In one embodiment, fingerprint sensor 1815 having an array
of PMUT pixels is comprised within always-on circuitry 1830 to
detect a touch of the ultrasonic fingerprint sensor by reading an
always-on first pixel subset of the array of PMUT pixels. In
response to detecting the touch using the always-on first pixel
subset, a second pixel subset is activated to determine if the
touch is associated with a human finger. In one embodiment, the
second pixel subset is activated in response to detecting a touch
of something consistent with a human finger. Always-on circuitry
1830 includes circuitry to respond to a determination that the
touch is associated with a human finger and trigger a move from the
first pixel subset to activating the second pixel subset, including
activating all of the array of PMUT pixels in the ultrasonic
fingerprint sensor to capture an image of the fingerprint of a
detected finger.
[0098] For example, the use of ultrasonic circuitry allows for low
power operation of a fingerprint sensor 1815. For example, a PMUT
array can operate in a first low power mode to detect a touch on
the ultrasonic fingerprint sensor by reading an always-on first
pixel subset of the array of PMUT pixels. In response to detecting
the touch using the always-on first pixel subset, the PMUT array is
switched to operate in a second low power mode using a second pixel
subset activated to determine if the touch is associated with a
human finger. If characteristics of a fingerprint, such as ridges
or valleys, are detected the PMUT array switches into operating in
a full power mode. It should be appreciated that the activation in
full-power mode may be instantiated by either the always-on
circuitry 1830 or the system circuitry 1840. In one embodiment,
substantially all of the PMUT devices of the array of fingerprint
sensor 1815 are used to analyze the image of a fingerprint
associated with the human finger. After completion of fingerprint
scanning, the PMUT array can be switched back to low power
operation.
[0099] FIG. 19 illustrates example operation in a first phase of a
finger detection mode associated with a two-dimensional array 1900
of ultrasonic transducers, according to some embodiments. In one
embodiment, the first phase of the finger detection mode includes
the activation of a first subset of ultrasonic transducers for
capturing single pixels (e.g., pixel 1910) within a block (e.g.,
block 1920) of two-dimensional array 1900. For example,
two-dimensional array 1900 includes twelve blocks of 24.times.24
ultrasonic devices. As illustrated, the first phase includes
activation of ultrasonic devices of the middle eight 24.times.24
blocks 1920 of ultrasonic transducers for capturing a single pixel
within each activated block. While the illustrated embodiment shows
only eight of the twelve blocks activated, and only ultrasonic
transducers activated for capturing a single pixel within the
activated blocks, it should be appreciated that any number of
blocks may be activated, that the pixel may be located at any
position within a block, and any number of ultrasonic transducers
may be activated for capturing any number of pixels, and that the
illustrated embodiment is an example of many different
possibilities. Moreover, it should be appreciated that the
two-dimensional array can include any number of ultrasonic
transducers, and the two-dimensional array may be divided into any
number of independently operable blocks. Furthermore, as described
above, embodiments described herein provide for utilizing multiple
ultrasonic transducers, some of which may be time-delayed relative
to each other, to focus a transmit beam to capture a pixel of an
image.
[0100] In the illustrated embodiment, pixel 1910 is periodically
captured in the first phase of the finger detection mode. Although
a single pixel is illustrated, it will be understood that multiple
pixels can be used, either grouped together or distributed
throughout the array. Also, each pixel may be imaged by activating
a plurality of PMUTs around the pixel. When a significant change in
ultrasonic wave receive intensity occurs due to the presence of an
object positioned near a sensor platen (not shown), circuitry is
activated to switch the pixel array out of the first low power
mode. In one embodiment, the first phase includes activating a
small subset of the pixels in the array in a highly duty-cycled
manner. For example, as illustrated, the 8-pixel pattern
illustrated in FIG. 19 is activated. In various embodiments, these
pixels are operated at a rate of 50-100 samples/second. On each
transmit/receive cycle, the signal from each pixel would be
compared to a threshold (e.g., a single value or an offset
plus/minus a range). For example, if the signal on M or more pixels
exceeds a single value, the system will proceed to a second phase
of the finger detection mode (also referred to as FDMB). In another
example, if the signal on M or more pixels falls outside of an
offset plus/minus a range (where `M` is a programmable setting),
the system will proceed to a second phase of the finger detection
mode. Otherwise, the system will remain in the first phase of the
finger detection mode. It should be appreciated that many types of
thresholding may be performed. For example, in another embodiment,
a sum of the received signals may be compared with a threshold, the
received signals may be divided into groups and compared to a
threshold, etc.
[0101] In various embodiments, a position of the pixel captured
during the first phase of the finger detection mode is moved during
the first phase of the finger detection mode. For example, using
the same pixel may increase the likelihood of a false reading, as
the features or position of the pixel may not be indicative of
contact or lack of contact with the array. Moreover, sensor
lifetime may be reduced by excessive usage of the same ultrasonic
sensors of the array. Imaging different pixels of the array may
improve the accuracy of the first phase of the finger detection
mode
[0102] In some embodiments, the pixel selection sequence is random
within an array or blocks of an array. In other embodiments, the
pixel selection sequence is deterministic within an array or blocks
of an array. In some embodiments, consecutive pixels (e.g., from
left to right and proceeding to the next lower row of pixels) are
selected. In other embodiments the ordering of selected pixels is
performed according a predetermined order. In some embodiments, all
pixels are selected before a pixel selection sequence is completed
(e.g., each pixel is selected once before a pixel can be selected
again). It should be appreciated that any ordering of pixel
selection sequence can be used.
[0103] In some embodiments, the pixel selection is constrained to a
subset of pixels of an array or a block. For example, pixel
selection may be constrained to pixels within a particular region
of a block. In a particular example, consider a 24.times.24 block
of ultrasonic devices (e.g., block 1920 of FIG. 19). In one
embodiment, pixel selection is constrained to the middle
16.times.16 pixels of the block. In the current example, the pixel
selection sequence is performed for each pixel of the 16.times.16
blocks (totaling 256 pixels) before the pixel selection sequence is
repeated.
[0104] As described herein, the first phase of the finger detection
is operable to determine whether an object has come in contact with
or interacted with a fingerprint sensor. In this manner, if it is
not determined that an object has interacted with the fingerprint
sensor (e.g., the change in ultrasonic wave intensity does exceed a
threshold), then the fingerprint sensor remains in the first phase
of the finger detection mode. In various embodiments, the first
phase of the finger detection mode only activates ultrasonic
transducers for capturing a small number of pixels, thus requiring
a low amount of power relative to the full operation of the
fingerprint sensor.
[0105] FIG. 20 illustrates an example duty-cycle timeline 2000 for
the first phase of the finger detection mode, according to an
embodiment. As illustrated, fingerprint sensor powers-up the
ultrasonic transducers for capturing the particular pixels,
transmits (Tx) an ultrasonic signal, receives (Rx) an ultrasonic
signal, performs an analog to digital (ADC) conversion of the
received ultrasonic signal, and compares the digital signal to a
stored threshold. For example, this process may take 1-100 .mu.s.
If the threshold range is not exceeded, the fingerprint sensor
enters a sleep state for a period (e.g., 10-20 ms). This cycle is
repeated until the threshold comparison results in detecting an
object contacting or interacting with the fingerprint sensor as
indicated by exceeding the threshold range.
[0106] FIG. 21 illustrates an example of thresholding 2100 for the
first phase of the finger detection mode, in accordance with
various embodiments. In various embodiments, the threshold is
described herein as an offset plus/minus a range. In other
embodiments, the threshold includes a range from a low threshold to
a high threshold. As illustrated, the thresholding for four example
pixels (pixel0 , pixel1, pixel2, and pixel3) is shown. The bar
represents the reflected signal received at the ultrasonic
transducer. As shown, the received signals for pixel0, pixel1 and
pixel2 all fall within the offset plus/minus the range. For
example, the signal received for pixel0 exceeds offset0, but falls
within the bounds of range0. Similarly, the signal received for
pixel1 and pixel2 each are less than offset1 and offset2,
respectively, but still fall within the bounds of range1 and
range2, respectively. However, the signal received for pixel3 falls
outside of the bounds of range3, indicating that at least that
portion of the fingerprint sensor has interacted with an
object.
[0107] In various embodiments, if it is determined that the signal
received for one pixel falls outside of the range, the finger
detection mode proceeds to the second phase. In other embodiments,
the finger detection mode proceeds to the second phase if the
signal received for a certain number of pixels fall outside of the
threshold range. For example, the fingerprint sensor may be
configured to proceed to the second phase if it is determined that
three pixels fall outside of the threshold range. It should be
appreciated that the number of pixels having received signals
falling outside of the threshold range is configurable, and that
any value may be set. It should also be appreciated that other
types of stimuli may cause a signal of the fingerprint sensor to
fall outside of a threshold. For example, applying a stress to the
fingerprint sensor (e.g., bending a phone housing the fingerprint
sensor in a back pocket) or thermal shock (e.g., dropping a phone
housing the fingerprint sensor in the snow) may cause the signal to
exceed the threshold. Even in these examples of different types of
stimuli, the finger detection mode would proceed to a second phase,
at least for purposes of updating threshold values.
[0108] In some embodiments, the first phase of the finger detection
is operable to detect whether a human finger has interacted with
the fingerprint sensor. For example, the acoustic properties of
many materials, such as acrylic, metal, cloth, nylon, etc., have
acoustic properties that are significantly different from a human
finger that impact the reflection intensity of the ultrasonic
signal. By properly determining a threshold, it is possible
determine that an object contacting the fingerprint sensor is not a
finger, thus rejecting phantom contact made from materials other
than human skin.
[0109] In certain embodiments described with respect to FIG. 22,
the finger detection mode is switched to a second low power mode
(e.g., second phase) to determine if the object is a finger. In one
embodiment, the second phase has a greater number of captured
pixels and an associated power usage greater than the first phase.
In other embodiments, the finger detection mode can be switched to
a full power, fingerprint sensor mode, to immediately attempt
detection of a fingerprint image. Once a fingerprint image is
obtained, or if a finger is determined not to be present, the pixel
array can be switched back to the always-on first low power
mode.
[0110] FIG. 22 illustrates example operation in a second phase of a
finger detection mode associated with a two-dimensional array 1900
of ultrasonic transducers, according to some embodiments. In one
embodiment, the second phase of the finger detection mode includes
the activation of a second subset of ultrasonic transducers for
capturing multiple pixels (e.g., pixels 2210) within a block (e.g.,
block 1920) of two-dimensional array 1900. In one embodiment, the
multiple pixels may be arranged in orthogonal vectors. For example,
two-dimensional array 1900 includes twelve blocks of 24.times.24
ultrasonic devices. As illustrated, the second phase includes
activation of ultrasonic devices of the middle eight 24.times.24
blocks of ultrasonic transducers for capturing a multiple pixels
within each activated block. While the illustrated embodiment shows
only eight of the twelve blocks activated, and only ultrasonic
transducers activated for capturing particular pixels within the
activated blocks, it should be appreciated that any number of
blocks may be activated, that the pixels may be located at any
position within a block, and any number of ultrasonic transducers
may be activated for capturing any number of pixels, and that the
illustrated embodiment is an example of many different
possibilities. Moreover, it should be appreciated that the
two-dimensional array can include any number of ultrasonic
transducers, and the two-dimensional array may be divided into any
number of independently operable blocks. Furthermore, as described
above, embodiments described herein provide for utilizing multiple
ultrasonic transducers, some of which may be time-delayed relative
to each other, to focus a transmit beam to capture a pixel of an
image.
[0111] In various embodiments, in the second phase of the finger
detection mode, a larger subset of pixels in the two-dimensional
array is captured in order to check for the presence of fingerprint
characteristics (e.g., ridges and valleys). In some embodiments,
because the fingerprint characteristics may be at any angle with
respect to the fingerprint array, the active pixels in second phase
will span multiple rows and multiple columns of the two-dimensional
array. It should be appreciated that, in accordance with various
embodiments, the second phase of finger detection mode may include
more than one intermediate phase. For example, the second phase may
include two successively larger subsets of pixels, wherein the
first is for identifying some finger-like features and the second
is for identifying a ridge/valley pattern.
[0112] In the illustrated embodiment, the captured pixels are
arranged in orthogonal vectors. As illustrated, an L-shaped pixel
pattern 2210 is shown and includes two orthogonally oriented twelve
pixel lines. In another embodiment, the orthogonal vectors are
arranged in a cross shaped pixel pattern. In another embodiment,
the orthogonal vectors may adapt to different arrangements during
the second phase of the finger detestation mode (e.g., rotate a
cross shaped pixel pattern about a center pixel, alternate between
a cross shaped pixel pattern and an L-shaped pixel pattern. It
should be appreciated that other pixel patterns of orthogonal
vectors may be used, including both intersecting orthogonal vectors
and non-intersecting orthogonal vectors. This illustrated
embodiment has sufficient size and orientation to detect a
characteristic ridge or valley of a fingerprint regardless of
orientation of the finger to the device. Although an L-shaped pixel
pattern is illustrated consisting of 23 total pixels, it will be
understood that alternative pixel patterns and pixel counts can be
used, and multiple pixel patterns can be either grouped together or
distributed throughout the array. In this second phase of the
finger detection mode, one or more transmit and receive cycles are
employed to determine if the object has a reflection intensity
consistent with a finger, and specifically whether the reflection
intensity along a line is consistent with the characteristic
spacing found in fingerprint ridges and valleys. If reflection
patterns consistent with a finger are detected, the mode can be
switched to turn on substantially all of the ultrasonic transducers
of the two-dimensional array to analyze biometric data associated
with the human finger, including subdermal layers, vein or artery
position, and a fingerprint image. Once a fingerprint image is
obtained, or if a finger is determined not to be present, the pixel
array can be switched back to the always-on first low power mode.
In one embodiment, if a finger is not determined to be present, the
offset of the threshold is updated with the most recent received
signal value for the pixel.
[0113] In accordance with various embodiments, a positioning pixel
that is representative of a position of the pixel pattern is used
to determine the pixel pattern selection sequence. The positioning
pixel of a pixel pattern may be any pixel of the pixel pattern, so
long as the selected positioning pixel remains constant within the
pixel pattern. In some embodiments, where the pixel pattern
includes orthogonal vectors, the intersecting pixel of the vectors
may be used as the positioning pixel. For example, the positioning
pixel may be the center pixel of a cross shaped pixel pattern or
the intersecting pixel of an L-shaped pixel pattern. In other
embodiments, the positioning pixel may be the center pixel of a
block defined by the orthogonal vectors, and may not be included in
the orthogonal vectors (e.g., the positioning pixel need not be
imaged).
[0114] In some embodiments, consecutive positioning pixels (e.g.,
from left to right and proceeding to the next lower row of pixels)
are selected during the pixel pattern selection sequence. In other
embodiments the ordering of selected positioning pixels is
performed according a predetermined order. In some embodiments, all
pixels within a block/array are selected as a positioning pixel
before a pixel pattern selection sequence is completed (e.g., each
pixel is selected as a positioning pixel once before a pixel can be
selected again). It should be appreciated that any ordering of
pixel pattern selection sequence can be used.
[0115] In some embodiments, the pixel pattern selection is
performed such that the positioning pixel is constrained to a
subset of pixels of an array or a block. For example, the
positioning pixel may be constrained to pixels within a particular
region of a block. In a particular example, consider a 24.times.24
block of ultrasonic devices (e.g., block 1920 of FIG. 22). In one
embodiment, positioning pixel selection is constrained to the
middle 16.times.16 pixels of the block. In the current example, the
pixel pattern selection sequence is performed for each pixel of the
16.times.16 block as positioning pixel (totaling 256 pixels) before
the pixel pattern selection sequence is repeated.
[0116] FIG. 23 illustrates an example duty-cycle timeline 2300 for
the second phase of the finger detection mode. The first phase of
the finger mode detection (e.g., FDMA) transitions to the second
phase of the finger mode detection (e.g., FDMB). As illustrated,
capture of reflected ultrasonic waves can require a paired series
of transmit (Tx) and receive (Rx) cycles. Between each signal pair,
analog to digital conversion (ADC) occurs, and the results are
transmitted for further digital processing. This capture cycle can
be repeated a number of times (e.g., 10-40 capture cycles).
[0117] After pixels of the second phase are captured, the received
data is processed to identify characteristics of a fingerprint. In
one embodiment, the received data is analyzed to identify if
ridge-valley-ridge or valley-ridge-valley patterns exist in the
scanned rows and columns. If no patterns exist, the system will
return to first phase of the finger detection mode (e.g., FDMA). In
this case, the system may update the first phase of the finger
detection mode thresholds to avoid entering second phase of the
finger detection mode again on the same stimulus. This prevents the
system from toggling back and forth between first phase and the
second when no finger is present. If a ridge/valley pattern is
recognized in the second phase of the finger detection mode, then
the system will exit finger detect mode and proceed to a full
fingerprint capture.
[0118] In various embodiments, the captured data of the second
phase of the finger detection mode is divided into groups of
pixels. FIG. 24 illustrates an example of thresholding 2400 for the
second phase of the finger detection mode, in accordance with
various embodiments. In the example of FIG. 22 there are 16 groups:
8 row groups, and 8 column groups. Each group includes 12 pixels.
In one example, detecting ridge-valley patterns within a given
group of pixels proceeds as follows: [0119] 1. Subtract the mean of
the group of pixels [0120] 2. Compare the result to .+-.range
values. [0121] a. If no pixels are outside of .+-.range, no
ridge/valley pattern is detected. End processing for this group of
pixels [0122] b. Otherwise, proceed to step 3 [0123] 3. Truncate
each pixel value's value to a single-bit (e.g., `1` if above the
mean, `0` if below the mean) [0124] 4. Check for patterns that
contain x"00"x"11"x"00"x or x"11"x"00"x"11"x, where `x` corresponds
to an arbitrary number of 0's or 1's (including none), [0125] a. If
neither pattern matches, no ridge/valley patterns are detected in
this pixel group [0126] b. If at least one pattern matches, then
ridge/valley patterns are detected
[0127] This procedure is performed for each pixel group in the
second phase of the finger detection mode scan to determine how
many of the groups contain ridge/valley patterns. If the number of
pixel groups that contain ridge/valley patterns equals or exceeds a
target count value `N`, the system will proceed to capture mode.
Otherwise, the system may update first phase of the finger
detection mode threshold offsets to be equal to the first phase of
the finger detection mode scan results and return to first phase of
the finger detection mode.
[0128] In another embodiment, an exclusive or (XOR) operation is
performed on neighboring pixel values to identify characteristics
of a fingerprint. In one embodiment, in the second phase of the
finger detection mode, an XOR operation is performed for each
element and the element next to it to detect whether there is a
"ridge-valley" or "valley-ridge" transition (e.g., XOR(1,0)=1,
XOR(0,1)=1). For example, where a value of 0 indicates a signal
below threshold (ridge) and a value of 1 indicates a signal above
threshold (valley), the following pattern is indicative of two
transitions: [0129] 0000011111100000
[0130] In one embodiment, a "despike" operation is performed. A
despike operation removes false indications of ridge-valley spikes
that result from noise when the contrast to noise ratio (CNR) is
low. For example, the following pattern includes false indications
of transitions: [0131] 0101000111011100010100
[0132] In this example, the first seven values "0101000" and the
final eight values "00010100" indicate real ridges and the middle
seven values "1110111" indicate a real valley. However, there are
random "1s" within the ridges and a random "0" within the valley
due to noise. The despike operation removes the random "1s" and
random "0s" by making any patterns containing "010" into "000" and
containing "101" into "111". After performing the despike
operation, the pattern will become: [0133]
0000000111111100000000
[0134] In various embodiments, within a block, a threshold is set
to determine how many blocks pass the test. For example, 4 out of 8
blocks may have more than 2 "XOR=1." The sum of all "XOR=1" will be
determined among all blocks (e.g., sum value equals X), which is
compared to a global threshold Y to determine whether X is greater
than Y. If X is greater than Y, it is determined that
characteristics of a fingerprint are identified.
[0135] FIGS. 25A-D illustrate another example of thresholding for
the second phase of the finger detection mode, in accordance with
various embodiments. In various embodiments, orthogonal vectors of
pixels are captured for detecting ridges and valleys, indicative of
a fingerprint image. In one embodiment, the orthogonal vectors are
arranged in a cross shaped pixel pattern. In another embodiment,
the orthogonal vectors are arranged in an L-shaped pixel pattern.
It should be appreciated that other pixel patterns of orthogonal
vectors may be used, including both intersecting orthogonal vectors
and non-intersecting orthogonal vectors.
[0136] As illustrated in FIG. 25A, ridges and valleys for each
orthogonal vector are detected out of the mean intensity level
within a threshold range. As illustrated in FIG. 25B, a vertical
profile of the finger may appear flattened due to high finger
pressure on an array of ultrasonic transducers, where ridges of a
finger are compressed. Points 2510a and 2510b indicate where the
curve (e.g., the pixel value) exceeds the mean plus threshold
value, indicative of a rising edge transition, and points 2510c and
2510d indicate where the curve drops below the mean minus threshold
value. In one embodiment, to detect and measure a ridge to ridge
size, a period between points 2510a and 2510b is computed. Only if
a point under the mean minus threshold is detected between points
2510a and 2510b is a ridge to ridge size determined. As
illustrated, point 2510d satisfies this requirement. FIG. 25C
illustrates the overlapping curves of FIGS. 25A and 25B.
[0137] FIG. 25D illustrates an example where a finger is pushed
against a fingerprint sensor with low pressure. Points 2520a and
2520b indicate where the curve (e.g., the pixel value) exceeds the
mean plus threshold value, indicative of a rising edge transition,
and points 2520c and 2520d indicate where the curve drops below the
mean minus threshold value. In one embodiment, to detect and
measure a ridge to ridge size, a period between points 2520a and
2520b is computed. Only if a point under the mean minus threshold
is detected between points 2520a and 2520b is a ridge to ridge size
determined. As illustrated, point 2520c satisfies this requirement.
FIGS. 25A-25D describe an example thresholding where a pattern
indicative of a fingerprint can be detected independent of finger
pressure.
[0138] FIGS. 26 through 28 illustrate flow diagrams of example
methods for operating a fingerprint sensor comprised of ultrasonic
transducers, according to various embodiments. Procedures of this
method will be described with reference to elements and/or
components of various figures described herein. It is appreciated
that in some embodiments, the procedures may be performed in a
different order than described, that some of the described
procedures may not be performed, and/or that one or more additional
procedures to those described may be performed. The flow diagrams
include some procedures that, in various embodiments, are carried
out by one or more processors under the control of
computer-readable and computer-executable instructions that are
stored on non-transitory computer-readable storage media. It is
further appreciated that one or more procedures described in the
flow diagrams may be implemented in hardware, or a combination of
hardware with firmware and/or software.
[0139] With reference to FIG. 26, at procedure 2610 of flow diagram
2600, a first subset of ultrasonic transducers of the fingerprint
sensor (e.g., fingerprint sensor 1815) are activated, where the
first subset of ultrasonic transducers is for detecting interaction
between an object and the fingerprint sensor. In one embodiment,
the ultrasonic transducers are PMUT devices. In one embodiment,
procedure 2610 is performed periodically until interaction between
an object and the fingerprint sensor is detected.
[0140] With reference to FIG. 27, flow diagram 2700 is shown in
which an embodiment of procedure 2610 is described. In one
embodiment, as shown at procedure 2710, a pixel (e.g., pixel 1910)
is captured using the first subset of ultrasonic transducers. In
one embodiment, where the plurality of ultrasonic transducers is
arranged into a plurality of blocks, a pixel for at least two
blocks (e.g., block 1920) of the plurality of blocks is captured.
At procedure 2720, a signal of the pixel is compared to a
threshold. In one embodiment, the threshold includes an offset and
a range. At procedure 2730, provided the signal is outside the
threshold, it is determined that interaction between an object and
the fingerprint sensor is detected.
[0141] With reference to FIG. 26, at procedure 2615, it is
determined whether an interaction between an object and the
fingerprint sensor has been detected. Provided an interaction
between an object and the fingerprint sensor is not detected, in
accordance with one embodiment, flow diagram 2600 proceeds to
procedure 2620. At procedure 2620, the fingerprint sensor enters a
sleep mode for a predetermined time (e.g., 10 to 20 ms). After the
predetermined time, flow diagram 2600 proceeds to procedure
2610.
[0142] With reference to procedure 2615, subsequent an interaction
between an object and the fingerprint sensor being detected, flow
diagram 2600 proceeds to procedure 2630. At procedure 2630, a
second subset of ultrasonic transducers of the fingerprint sensor,
where the second subset of ultrasonic transducers is for
determining whether the object is a human finger, wherein the
second subset of ultrasonic transducers comprises a greater number
of ultrasonic transducers than the first subset of ultrasonic
transducers.
[0143] With reference to FIG. 28, flow diagram 2800 is shown in
which an embodiment of procedure 2630 is described. In one
embodiment, as shown at procedure 2810, a plurality of pixels
(e.g., pixels 2210) arranged to detect characteristics of a
fingerprint on the object is captured. In one embodiment, the
plurality of pixels is arranged in orthogonal vectors. In one
embodiment, the orthogonal vectors are arranged in an L-shaped
pixel pattern. In another embodiment, the orthogonal vectors are
arranged in a cross shaped pixel pattern. In another embodiment,
the orthogonal vectors may adapt to different arrangements during
the second phase of the finger detestation mode (e.g., rotate a
cross shaped pixel pattern about a center pixel, alternate between
a cross shaped pixel pattern and an L-shaped pixel pattern. It
should be appreciated that other pixel patterns of orthogonal
vectors may be used, including both intersecting orthogonal vectors
and non-intersecting orthogonal vectors. In one embodiment, where
the plurality of ultrasonic transducers is arranged into a
plurality of blocks, orthogonal vectors of pixels for at one block
of the plurality of blocks are captured. At procedure 2820, it is
determined whether the plurality of pixels comprises
characteristics of a fingerprint. In one embodiment, as shown at
procedure 2830, it is determined whether the plurality of pixels is
indicative of a ridge/valley pattern. At procedure 2840, provided
the plurality of pixels comprises characteristics of a fingerprint,
it is determined that the object is a human finger.
[0144] With reference to FIG. 26, at procedure 2635, it is
determined whether the object is a finger. Provided the object is
not a finger, in accordance with one embodiment, flow diagram 2600
proceeds to procedure 2640. At procedure 2640, the threshold is
updated based on the signal. In one embodiment, the offset of the
threshold is updated. In one embodiment, flow diagram 2600 then
proceeds to procedure 2620. In another embodiment, flow diagram
2600 then proceeds to procedure 2610.
[0145] In one embodiment, provided the object is determined to be a
finger, flow diagram 2600 proceeds to procedure 2645. At procedure
2645, an image of a fingerprint of the finger is captured. In one
embodiment, as shown at procedure 2650, the image of the
fingerprint is transmitted to a host processor. In one embodiment,
flow diagram 2600 then proceeds to procedure 2620. In another
embodiment, flow diagram 2600 then proceeds to procedure 2610.
[0146] What has been described above includes examples of the
subject disclosure. It is, of course, not possible to describe
every conceivable combination of components or methodologies for
purposes of describing the subject matter, but it is to be
appreciated that many further combinations and permutations of the
subject disclosure are possible. Accordingly, the claimed subject
matter is intended to embrace all such alterations, modifications,
and variations that fall within the spirit and scope of the
appended claims.
[0147] In particular and in regard to the various functions
performed by the above described components, devices, circuits,
systems and the like, the terms (including a reference to a
"means") used to describe such components are intended to
correspond, unless otherwise indicated, to any component which
performs the specified function of the described component (e.g., a
functional equivalent), even though not structurally equivalent to
the disclosed structure, which performs the function in the herein
illustrated exemplary aspects of the claimed subject matter.
[0148] The aforementioned systems and components have been
described with respect to interaction between several components.
It can be appreciated that such systems and components can include
those components or specified sub-components, some of the specified
components or sub-components, and/or additional components, and
according to various permutations and combinations of the
foregoing. Sub-components can also be implemented as components
communicatively coupled to other components rather than included
within parent components (hierarchical). Additionally, it should be
noted that one or more components may be combined into a single
component providing aggregate functionality or divided into several
separate sub-components. Any components described herein may also
interact with one or more other components not specifically
described herein.
[0149] In addition, while a particular feature of the subject
innovation may have been disclosed with respect to only one of
several implementations, such feature may be combined with one or
more other features of the other implementations as may be desired
and advantageous for any given or particular application.
Furthermore, to the extent that the terms "includes," "including,"
"has," "contains," variants thereof, and other similar words are
used in either the detailed description or the claims, these terms
are intended to be inclusive in a manner similar to the term
"comprising" as an open transition word without precluding any
additional or other elements.
[0150] Thus, the embodiments and examples set forth herein were
presented in order to best explain various selected embodiments of
the present invention and its particular application and to thereby
enable those skilled in the art to make and use embodiments of the
invention. However, those skilled in the art will recognize that
the foregoing description and examples have been presented for the
purposes of illustration and example only. The description as set
forth is not intended to be exhaustive or to limit the embodiments
of the invention to the precise form disclosed.
* * * * *